I was wondering what other benefits 3.25" wheels have over 4" other than more viability in gearing. Especially for this season, is it truly necessary or can I do just fine with a 4"? Thanks!
Actually, there is really no huge advantage of 3.25" over 4" wheels, and vice versa.
It all depends on the use case and what you want to achieve.
So I would suggest that you go back to the game analysis and design considerations to see which size wheels suit your needs better.
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It’s really up to you. 3.25” can offer some nice vertical space if you want to make a small bot, but other than that and gearing/speed/torque ratios theres really not much of a difference. Do what you think is best for your robot as in the end, it really goes down to how well you can drive it.
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I’m my experience, the main advantage of smaller wheels is the lower center of gravity. A low COG will mean less tipping over, less wheelies, and better mechanical advantage when in a push fight. I am using 4 inch wheels to accommodate the special gearing I am using. If you need a good drivetrain for 3.25 wheels, try 360 rpm.
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Another advantage of 3.25 is actually acceleration. In theory, if the gear ratios balance out, it should be the same, but accelleration in practice usually is better on smaller wheels.
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COG is not dependent on wheel size… (thinking - yeah, nope)… CoG is dependent on distribution of mass in relation of height of structure … but best to consider center of mass.
Here you go!
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Yes, this is true, but assuming your robot structure stays the same, the larger wheel will mean a higher robot. There are accomodations you can make to have a low CoG on 4 inch wheels, but at that point you’re better off just saving some trouble and using 2.75s.
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not certain - tell me how much the wheel is lifting frame off the ground? That elevation is what impact center of mass… not diameter of wheel used… experiment and provide test results 
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Yeah… I was thinking the same as well,
It should just be less than 0.4” difference,
And considering the drive train section is normally heavy, don’t think the CG (or CM) will move significantly.
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I see what you are saying @meng and @lacsap that the difference is minute. However, the drivetrain I am using is 4 inch wheels but they’re mounted so that the CoG is unnecessarily high. I haven’t had any problems with it and it gives me plenty of space to build stuff like an intake.
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There’s also nothing stopping you from mounting everything lower than the middle of the 4” wheels. you could have the exact same COG on any wheel size. It just depends on how you build it. Yes, in the most simple chassis possible the cog will a little higher on 4” wheels compared to the others. but if you plan around it, you can make COG whatever you feel like on any wheel size
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